1. Field of the Invention
This invention relates to the field of data processing, and, more particularly, to improved non-volatile shift register having amorphous silicon thin-film floating-gate transistors which non-volatilely store data in the event power is turned off or lost.
2. Description of Related Art
Amorphous thin-film transistors provide a technology that is advantageous for large area, low cost integrated circuits. One type of such transistors has a floating gate that can be used to provide non-volatile storage of data. There are many different devices commonly used in digital circuits which temporarily store data and wherein the data is lost when power is turned off and in the event of a power failure. Standard registers are examples of such devices. The invention is directed generally to an improved register in which amorphous silicon thin-film floating-gate transistors are used to buffer or temporarily store data while power is turned on and to non-volatilely store data in the event power is lost or turned off. The invention is also directed specifically to an improved shift register providing a serial-in, serial-out flow of data in which amorphous silicon thin-film floating-gate transistors are used to buffer or temporarily store the data while power is turned on and to non-volatilely store data in the event power is lost or turned off. Such preservation of the data may advantageously be used for diagnostic, start-up, and resume operations.
It is recognized that floating gate transistors have been implemented using crystalline semiconductor material. Such transistors are operated by injecting a charge onto the floating gate by means of an avalanche breakdown of the insulator surrounding the floating gate. Such transistors find use in erasable programmable read only memories (EPROM) where the injected charge can be non-volatilely stored for long periods of time when power is off. However, crystalline floating gate transistor devices have limited use otherwise since it requires a relatively long period of time to erase the charge and reprogram the device, and the insulator has a limited life due to the deleterious effect of the avalanche breakdown.